What do you want to know?
I've been about 8 times now, some friends live over in rural hungary.
Its nice, its cheap when you get away from the Pest side close to the danube which is the expensive side. Buda side of the river is classic tourist area for daytime visit, and Pest is the built up area. Nice restaurants, a lot around the Octogon area.
Get around by the tram system, where you buy a book of 10 tickets for about a tenner.
The spas are lovely, even better not in the heat, sitting in a heated pool in wintertime is superb. Quite a few around too.
Budapest can be a bit of a rough city, its one of those where I've felt a genuine chance of being pick pocketed, and its somewhere you don't sit down in a bar at a table full of empty glasses, they'll charge you for each of those as a drink. Worth reading about that side of thing before going so you can know some of the tricks.
One thing is always change your money inside the country, buy a bit in advance for taxi and first night, but the best rate in the uk is not even close the worst airport rate you'll get there. A few years ago the post office was offering 282 forints to the pound, you got 309 inside the country...
Recently, due to their national airline going under, theres been a massive jump in available flights from uk. Used to be one from LHR, one from LGW, one from Luton, one from MAN. Now theres Ryanair doing Edinburgh, Manchester, Leeds Bradford, East Midlands and Birmingham. Easyjet doing a load from Luton too, and I think Wizzair was doing a bunch too. This might change in a month, they're closing Terminal 1 of Budapest airport, the one which is accessible by train and where a lot of the cheap airlines landed. The new ones land at T2, which was the normal airport which has real airport things like lounges, but not sensible public transport sadly...